This invention relates to the operation of yarn feed mechanisms for tufting machines and more particularly to a scroll-type pattern controlled yarn feed wherein each set of yarn feed rolls is driven by an independently controlled servo motor. In one embodiment, a scroll-type pattern controlled yarn feed is provided wherein each yarn may be directed to a separate yarn feed device, and each yarn feed device is driven by an independently controlled servo motor. In another embodiment, a scroll-type pattern controlled yarn feed is provided where a plurality of yarns is directed to a yarn feed device, each yarn feed device being driven by an independently controlled servo motor, and the yarns may be distributed across the tufting machine to selected needles by the use of a tube bank.
Pattern control yarn feed mechanisms for multiple needle tufting machines are well known in the art and may be generally characterized as either roll-type or scroll-type pattern attachments. Roll type attachments are typified by J. L. Card, U.S. Pat. No. 2,966,866 which disclosed a bank of four pairs of yarn feed rolls, each of which is selectively driven at a high speed or a low speed by the pattern control mechanism. All of the yarn feed rolls extend transversely the entire width of the tufting machine and are journaled at both ends. There are many limitations on roll-type pattern devices. Perhaps the most significant limitations are: (1) as a practical matter, there is not room on a tufting machine for more than about eight pairs of yarn feed rolls; (2) the yarn feed rolls can be driven at only one of two, or possibly three speeds, when the usual construction utilizing clutches is used—a wider selection of speeds is possible when using direct servo motor control, but powerful motors and high gear ratios are required and the shear mass involved makes quick stitch by stitch adjustments difficult; and (3) the threading and unthreading of the respective yarn feed rolls is very time consuming as yarns must be fed between the yarn feed rolls and cannot simply be slipped over the end of the rolls, although the split roll configuration of Watkins, U.S. Pat. No. 4,864,946 addresses this last problem.
The pattern control yarn feed rolls referred to as scroll-type pattern attachments are disclosed in J. L. Card, U.S. Pat. No. 2,862,465, are shown projecting transversely to the row of needles, although subsequent designs have been developed with the yarn feed rolls parallel to the row of needles as in Hammel, U.S. Pat. No. 3,847,098. Typical of scroll type attachments is the use of a tube bank to guide yarns from the yarn feed rolls on which they are threaded to the appropriate needle to form a series of pattern repeats across the width of the backing material. In this fashion yarn feed rolls need not extend transversely across the entire width of the tufting machine and it is physically possible to mount many more yarn feed rolls across the machine. Typically, scroll pattern attachments have between 36 and 120 sets of rolls, and by use of electrically operated clutches each set of rolls can select from two, or possibly three, different speeds for each stitch. The use of servo motor driven scroll attachments as described in U.S. Pat. Nos. 6,244,203 and 6,283,053 by Morgante, et al. has maximized the precision and variety of scroll type patterns available to the industry.
The use of yarn feed tubes introduces additional complexity and expense in the manufacture of the tufting machine; however, the greater problem is posed by the differing distances that yarns must travel through yarn feed tubes to their respective needles. Yarns passing through relatively longer tubes to relatively more distant needles suffer increased drag resistance and are not as responsive to changes in the yarn feed rates as yarns passing through relatively shorter tubes. Accordingly, in manufacturing tube banks, compromises have to be made between minimizing overall yarn drag by using the shortest tubes possible, and minimizing yarn feed differentials by utilizing the longest tube required for any single yarn for every yarn. Tube banks, however well designed, introduce significant additional cost in the manufacture of scroll-type pattern attachments. Attempts to maximize tube bank efficiency are reflected in U.S. Pat. No. 6,244,203 by Morgante and U.S. Pat. Nos. 6,834,601 and 5,983,815 by Card.
One solution to the tube bank problems, which also provides the ability to tuft full width patterns is the full repeat scroll invention of Bardsley, U.S. Pat. No. 5,182,997, which utilizes rocker bars to press yarns against or remove yarns from contact with yarn feed rolls that are moving at predetermined speeds. Yarns can be engaged with feed rolls moving at one of two preselected speeds, and while transitioning between rolls, yarns are briefly left disengaged, causing those yarns to be slightly underfed for the next stitch. The use of single end servo motor driven yarn feed attachments, as reflected in U.S. Pat. No. 6,283,053 by Morgante, et al. has maximized the versatility of full repeat patterns by providing a wide range of stitch heights for each stitch at each needle.
Thus a servo motor driven pattern device might run a high speed drive shaft to feed yarn at 0.9 inches per stitch if the needle bar does not shift, 1.0 inches if the needle bar shifts one gauge unit, and 1.1 inches if the needle bar shifts two gauge units. Other slight variations in yarn feed amounts are also desirable, for instance, when a yarn has been sewing low stitches and it is next to sew a high stitch, the yarn needs to be slightly overfed so that the high stitch will reach the full height of subsequent high stitches. Similarly, when a yarn has been sewing high stitches and it is next to sew a low stitch, the yarn needs to be slightly underfed so that the low stitch will be as low as the subsequent low stitches. Therefore, there is a need to provide a pattern control yarn feed device capable of producing scroll-type patterns and of feeding the yarns from each yarn feed roll at an individualized rate, without yarn slippage.
Due to the considerations of cost and space, it is desirable to utilize the smallest servo motors that are adequate in speed and torque to provide precise yarn feeds to the needles. In some instances, such as reflected in dual end servo scroll pattern attachments, using the same yarn drives as are designed for single end servo scroll pattern attachments typified by U.S. Pat. No. 6,877,447, it has been desirable to enhance the gear ratios so that the servo motors provide additional torque, and patterning is not adversely affected by snags as yarn is fed from a creel to the pattern attachment. Furthermore, some types of pattern attachments, such as the full repeat scroll of Bardsley, U.S. Pat. No. 5,182,997, only feed yarns by pressure against a drive roller and are susceptible to yarn slippage in the case of snags. Therefore, a method is needed to reduce the possibility of yarn slippage so that patterns can be more precisely tufted.